1. Field of the Invention
The present invention relates to filters, and more particularly to a filtering cartridge with a porous body of compacted and sintered noncorroding particles.
2. Description of the Related Art
In general, these types of filtering cartridges have a uniform pore structure and are utilized to filter out undesired particles from a liquid or gas. The undesired dispersed particles in the medium to be filtered arrive at the individual grains of the filtering cartridge through different transport mechanisms, such as screening effects, inertial forces, diffusion and electrostatic forces, while the remainder of the medium passes through the filtering cartridge. If the pores of the filtering cartridge are clogged by the filtrate, then the filtering cartridge is no longer operative and must be cleaned. As a rule, this cleaning is performed by reverse impulses in a counterflow of the medium.
Filtering cartridges must often be employed at high temperatures and for offensive media. For example, temperatures up to 1000.degree. C. can appear in dust extraction from hot process and exhaust gases. The filtering cartridges must therefore be resistant to both high temperatures and corrosion. In spite of the porosity necessary for the filter effect, the filtering cartridges must simultaneously have sufficient mechanical toughness in order to be easy to handle and, above all, to withstand without damage the mechanical stresses which occur from the shock-like reverse impulses for cleaning the filtering cartridge.
Currently, self-supporting filtering cartridges are used for high-performance extraction of dust from hot gases, mostly as a one-sided hollow cylinder, as a so-called candle made of ceramic material. Filtering cartridges of this type have excellent corrosion resistance and temperature resistance, but are indeed not well suited with regard to shock-like mechanical stress, so that a premature failure of filtering cartridges of this type often occurs from reverse impulses during the filter's mandatory cleaning.
Known metallic filtering cartridges indeed have a sufficient amount of the required mechanical toughness, but can no longer be satisfactorily used, especially for particularly offensive media and at high temperatures.
By way of example, DE-B2 24 56 626 describes a filtering cartridge made of an alloy with 30-40% chromium by weight, 2-4% silicon by weight and, except for small amounts of carbon and nitrogen, with iron as the remainder. Such a filtering cartridge is primarily used for polymerization liquefaction at temperatures of approximately 300.degree. C. and is only suitable to a limited extent for offensive media and higher temperatures.
Chromium is known as a metal with excellent corrosion resistance, even at high temperatures. Furthermore, it is also well known that pure chromium or alloys with a large chromium content normally are very brittle, and therefore do not fulfill the mechanical demands which are placed on filtering cartridges.
The alloy corresponding to DE-B2 24 56 626 is therefore limited to a maximum chromium content of 40% by weight, and no other filtering cartridges with a larger chromium content are known to be in practical operation.